13 research outputs found
Establishing a Au Nanoparticle Size Effect in the Oxidation of Cyclohexene Using Gradually Changing Au Catalysts
The effect of the size of gold nanoparticles
on their catalytic
activity in aerobic oxidation of cyclohexene was established using
supported gold nanoparticles that gradually undergo a change in size
during the catalytic reaction. Two triphenylphosphine-stabilized clusters,
Au<sub>9</sub>(PPh<sub>3</sub>)<sub>8</sub>(NO<sub>3</sub>)<sub>3</sub> and Au<sub>101</sub>(PPh<sub>3</sub>)<sub>21</sub>Cl<sub>5</sub>, were synthesized and deposited on SiO<sub>2</sub>. The clusters
did not retain their structure during the catalytic reaction; larger
particles with mean diameters of âŒ5â10 nm gradually
formed. By combining kinetic experiments with the monitoring of catalyst
transformations using transmission electron microscopy, diffuse-reflectance
ultravioletâvisible spectroscopy, and X-ray photoelectron spectroscopy,
we showed that catalytic activity appeared only after >2 nm Au<sup>0</sup> particles had formed, while intact clusters and phosphine-free
<2 nm particles were inactive in cyclohexene oxidation under the
studied conditions
Supported silver catalysts prepared via melt infiltration: Synthesis, characterization and performance in selective hydrogenation
Heterogeneous supported catalysts are often synthesized by impregnation or precipitation methods. Recently, melt infiltration has emerged as an alternative method that allows high metal loadings and eliminates the need for a solvent, but challenges arise regarding control over the particle size and distribution. In this work, melt infiltration for the synthesis of supported silver catalysts is explored. The narrow pore size distribution of the chosen ordered mesoporous silica support, SBA-15, allowed in depth in-situ and ex-situ characterization of the infiltration of the precursor, molten silver nitrate, into the support and its subsequent decomposition to form metallic silver nanowires or nanoparticles. The heat treatment parameters during decomposition played a key role in determining whether nanowires or nanoparticles were formed. The supported silver catalysts containing high silver weight loadings were investigated in the selective hydrogenation of cinnamaldehyde, where the silver nanowires showed superior activity and selectivity over the nanoparticles. Hence, melt infiltration shows great promise for the synthesis of supported silver catalysts containing high silver weight loadings, which are applicable in, e.g., selective oxidation or hydrogenation reactions
Supported silver catalysts prepared via melt infiltration: Synthesis, characterization and performance in selective hydrogenation
Heterogeneous supported catalysts are often synthesized by impregnation or precipitation methods. Recently, melt infiltration has emerged as an alternative method that allows high metal loadings and eliminates the need for a solvent, but challenges arise regarding control over the particle size and distribution. In this work, melt infiltration for the synthesis of supported silver catalysts is explored. The narrow pore size distribution of the chosen ordered mesoporous silica support, SBA-15, allowed in depth in-situ and ex-situ characterization of the infiltration of the precursor, molten silver nitrate, into the support and its subsequent decomposition to form metallic silver nanowires or nanoparticles. The heat treatment parameters during decomposition played a key role in determining whether nanowires or nanoparticles were formed. The supported silver catalysts containing high silver weight loadings were investigated in the selective hydrogenation of cinnamaldehyde, where the silver nanowires showed superior activity and selectivity over the nanoparticles. Hence, melt infiltration shows great promise for the synthesis of supported silver catalysts containing high silver weight loadings, which are applicable in, e.g., selective oxidation or hydrogenation reactions
Chemically synthesised atomically precise gold clusters deposited and activated on titania. Part II
Synchrotron XPS was used to investigate a series of chemically synthesised, atomically precise gold clusters Au(n)(PPh3)y (n = 8, 9 and 101, y depending on the cluster size) immobilized on anatase (titania) nanoparticles. Effects of post-deposition treatments were investigated by comparison of untreated samples with analogues that have been heat treated at 200 °C in O2, or in O2 followed by H2 atmosphere. XPS data shows that the phosphine ligands are oxidised upon heat treatment in O2. From the position of the Au 4f(7/2) peak it can be concluded that the clusters partially agglomerate immediately upon deposition. Heating in oxygen, and subsequently in hydrogen, leads to further agglomeration of the gold clusters. It is found that the pre-treatment plays a crucial role in the removal of ligands and agglomeration of the clusters.David P. Anderson, Rohul H. Adnan, Jason F. Alvino, Oliver Shipper, Baira Donoeva, Jan-Yves Ruzicka, Hassan Al Qahtani, Hugh H. Harris, Bruce Cowie, Jade B. Aitken, Vladimir B. Golovko, Gregory F. Metha and Gunther G. Andersso
Control of Gold Nanostructure Morphology by Variation of Temperature and Reagent Ratios in the Turkevich Reaction
Synthesis and Characterization of Multinuclear Manganese-Containing Tungstosilicates
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